FIGS. 6 to 9 show a connector disclosed in the following Patent Document 1.
As shown in FIG. 6, the connector 100 includes a first connector housing 110 and a second connector housing 120.
The first connector housing 110 includes a hood portion 111 and a lock arm 112. The hood portion 111 which is substantially shaped like a cylinder is fitted to an outer circumference of a cylindrical portion 121 of the second connector housing 120 serving as a connection counterpart. The lock arm 112 is formed integrally with the first connector housing 110.
The lock arm 112 includes an erect portion 113 and an arm body 114. The erect portion 113 rises from a position close to a base end (right end in FIG. 6) of the first connector housing 110. The arm body 114 extends toward a front end side of the hood portion 111 from a distal end of the erect portion 113. The arm body 114 is formed into a single-end supported beam shape in which a distal end 114a of the arm body 114 serves as a free end. When the first connector housing 110 and the second connector housing 120 are fitted to each other as shown in FIG. 8, the distal end 114a side of the arm body 114 is deflected and deformed in a direction (direction of an arrow X1 in FIG. 6 or direction of an arrow R1 in FIG. 8) substantially perpendicular to the surface of the cylindrical portion 121 which will be described later so that the distal end 114a side of the arm body 114 can allow a lock protrusion 122 of the second connector housing 120 to move.
In addition, the arm body 114 includes a cavity 114b engaged with the lock protrusion 122 of the second connector housing 120 which will be described later, in a position close to the free end.
A release arm 115 is formed integrally with the lock arm 112. The release arm 115 includes arm portions 115a and an operating portion 115b. The arm portions 115a extend toward the base end side of the first connector housing 110 from both end portions of the distal end 114a of the lock arm 112. Distal ends of the pair of arm portions 115a are connected to each other through the operating portion 115b. 
When the operating portion 115b of the release arm 115 is pushed down in a direction of an arrow Z1 as shown in FIG. 9, the arm portions 115a swing accordingly so that the distal end 114a of the lock arm 112 connected to base ends of the arm portions 115a can be displaced in a direction of an arrow R1. Accordingly, when the operating portion 115b of the release arm 115 is pushed down, engagement between the lock arm 112 and the lock protrusion 122 is released so that the connector housings can be disconnected from each other.
The second connector housing 120 includes the cylindrical portion 121 and the lock protrusion 122. The aforementioned hood portion 111 is fitted to the outer circumference of the cylindrical portion 121. The lock protrusion 122 is provided to protrude from an outer surface of the cylindrical portion 121. When a fitting length between the cylindrical portion 121 and the hood portion 111 reaches a predetermined value as shown in FIG. 9, the lock protrusion 122 is engaged with the lock arm 112 to thereby lock the fitting state between the first connector housing 110 and the second connector housing 120.